The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical automatic transmission includes a hydraulic control system that, among other functions, is employed to actuate a plurality of torque transmitting devices. These torque transmitting devices may be, for example, friction clutches and brakes or synchronizers. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as oil, to a plurality of valves and solenoids within a valve body. The main pump is driven by the engine of the motor vehicle. The valves and solenoids are operable to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the plurality of torque transmitting devices within the transmission. The pressurized hydraulic fluid delivered to the torque transmitting devices is used to engage or disengage the devices in order to obtain different gear ratios.
These torque transmitting actuation systems, which may include rotating seal rings, valves, and solenoids may have low, though not zero, fluid leakage. Accordingly a minimum volume of hydraulic fluid must be provided to these systems. In addition, various subsystems within the hydraulic control system require different levels of pressurization and flow rates. While conventional hydraulic control systems are effective at dealing with the leakage and with the different hydraulic demands of various subsystems, there is room in the art for improved hydraulic control circuits that reduce the amount of complex components while improving efficiency and controllability of the system.